1. Technical Field
The present invention relates to a method and test kit, or test slide, for sensing the presence of blood in stool specimens. More specifically, the present invention relates to an improved test slide incorporating test monitors for verifying the results of the test and for checking the effectiveness of a vegetable peroxidase denaturing solution.
2. Prior Art
Test slides or kits for determining the presence of blood in stool samples are useful in the early diagnosis of cancer of the digestive tract. Such test slides provide a convenient method by which a patient may send a stool specimen to a laboratory for analysis.
One form of such a test slide is disclosed in U.S. Pat. No. 3,996,006 to Pagano in which a test slide comprising a guaiac impregnated paper is enclosed in a multi-folded cardboard package having test areas which are accessible through a set of cardboard flaps formed in the top of the test slide. A patient using the test slide smears a small sample of a stool specimen on each of the test areas, closes the flaps and sends the test slide to a laboratory for analysis. When the test slide is received at the laboratory, a technician opens a flap in the bottom of the test slide to obtain access to the other side of the guaiac impregnated paper. The technician then applies a hydrogen peroxide developing solution to the guaiac impregnated paper. If occult blood is present in the sample, the blood will catalyze a chromogen reaction in the guaiac when exposed to the developing solution. If no blood is present in the sample the chromogen reaction should not occur and the test result would be negative.
To provide a check on the performance of the test reagent and developer solution U.S. Pat. No. 4,365,970 to Lawrence et al discloses the concept of imprinting a portion of the test slide bearing the test reagent with a small quantity of hemoglobin or hemin, a hemoglobin derived catalyst which reacts to adverse environmental conditions in a manner similar to hemoglobin. When the test slide is exposed to the developing solution the hemoglobin or hemin will normally cause the guaiac in that portion of the test slide to undergo the chromogen reaction as long as the guaiac and developing solution are performing properly and the hemoglobin or hemin has not decomposed or been denatured.
The use of hemoglobin or a derivative of hemoglobin, such as hemin, presents certain problems in the manufacture of test slides. Hemoglobin is an organic substance which is subject to decomposition or denaturation. A problem with use of a hemoglobin derivative is the danger of transmitting a venereal disease, hepatitis or another communicable disease capable of being transmitted with a blood sample. To reduce the risk of transmitting such a disease it has been necessary to test the hemoglobin or hemin prior to sending it to a printer to verify that no disease is carried by the substance.
Current scientific research suggests that the ingestion of foods including vegetable peroxidase may cause false indications of blood in a stool sample. After digestion of food including vegetable peroxidase is complete a certain residual amount of vegetable peroxidase is passed through the intestines and is included in the stool specimen. A solution to the problem proposed in U.S. Pat. No. 4,333,734 to Fleischer is to inactivate the vegetable peroxidase applying a denaturing, or inactivating, solution to the test slide prior to development. While this makes occult blood test slides more reliable, there is no way disclosed for determining whether the inactivating solution is effective in inhibiting the catalyzation of the guaiac by the residual vegetable peroxidase in the stool specimen.
If the test spot of Lawrence were used and a positive result was indicated by the test, it would not be possible to determine whether the positive result was caused by vegetable peroxidase or occult blood in the sample. In the event the vegetable peroxidase inhibiting solution is not effective, it would be possible to have a false positive test result caused by the presence of vegetable peroxidase which had not been neutralized. If a false positive test occurs, a patient may be subjected to unnecessary tests.
These and other problems encountered in using prior art test slides have been overcome according to the present invention.